PD-L1 antibody, antigen-binding fragment thereof and medical application thereof

ABSTRACT

The present invention relates to a PD-L1 antibody, antigen-binding fragments, and medical application thereof. Further, the present invention relates to chimeric antibodies and humanized antibodies comprising the CDR regions of the present PD-L1 antibody, as well as a pharmaceutical composition comprising the present PD-L1 antibody and the antigen-binding fragments thereof, and their use as anti-cancer drugs. In particular, the present invention relates to a humanized PD-L1 antibody and its use in preparation of a medicament for the treatment of PD-L1 mediated disease or disorder.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. application Ser. No. 15/775,598, filed May 11, 2018, which is a Section 371 of International Application No. PCT/CN2016/104320, filed Nov. 2, 2016, which was published in the Chinese language on May 26, 2017, under International Publication No. WO 2017/084495 A1, which claims priority under 35 U.S.C. § 119(b) to Chinese Application No. 201510788907.3, filed Nov. 17, 2015, the disclosures of which are incorporated herein by reference in their entirety.

REFERENCE TO SEQUENCE LISTING SUBMITTED ELECTRONICALLY

This application contains a sequence listing, which is submitted electronically via EFS-Web as an ASCII formatted sequence listing with a file name “065825_58US2_Sequence_Listing” and a creation date of Aug. 7, 2020, and having a size of about 49 kb. The sequence listing submitted via EFS-Web is part of the specification and is herein incorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to a PD-L1 antibody, antigen-binding fragment thereof, a chimeric antibody, and a humanized antibody comprising the CDR regions of a PD-L1 antibody, as well as a pharmaceutical composition comprising a PD-L1 antibody or an antigen-binding fragment thereof, and its use as an anti-cancer drug.

BACKGROUND OF THE INVENTION

Tumor immunotherapy has been a hot area in tumor therapeutics for a long time, wherein T cell-associated immunotherapy is one of the main pillars. Tumor immunotherapy kills tumors by fully utilizing and mobilizing cytotoxic T lymphocytes in patients. It may be the most effective and safest way for cancer treatment. At the same time, tumor escape is a huge obstacle faced by tumor immunotherapy, in which the rapid proliferation of the cancer cells is promoted via their inhibitory effect on the immune system.

There is an extremely complicated relationship between the mechanism underlying the tumor immune escape and the body's immune response to tumors. In the early stages of tumor immunotherapy, tumor-specific killer T cells have biological activity, but lose the killing function as the tumor progresses into late stages. Thus, tumor immunotherapy is aimed to maximize the patient's own immune system response to the tumor. It is essential in tumor immunotherapy to not only activate the innate immune system response, but also maintain the duration and intensity of the immune response.

A human T-cell is activated in vivo via a two-signaling-pathway system, wherein antigen-presenting cells are needed to present MHC-antigen peptide to T cells to provide a first signal. Then a series of co-stimulatory molecules are required to provide a second signal to enable T cells to exhibit a normal immune response. This double-signaling system plays a vital role in balancing the in vivo immune system and strictly regulates different immune responses to endogenous and exogenous antigens, respectively. The absence of a second signal provided by co-stimulatory molecules will result in no response or sustained-specific T cell immune response and consequently lead to tolerance. Therefore, the second signaling pathway plays a key regulatory role in the whole process of the immune response.

Programmed death-1 (PD-1), found in 1992, is a protein receptor expressed on the surface of T cells and is involved in cell apoptosis. PD-1 belongs to the CD28 family and exhibits 23% homology in amino acid sequence with cytotoxic T lymphocyte antigen 4 (CTLA-4). Unlike CTLA4, PD-1 is mainly expressed on the activated T cells, B cells and myeloid cells. PD-1 has two ligands, PD-L1 and PD-L2. PD-L1 is mainly expressed on the T cells, B cells, macrophages, and dendritic cells (DC), and the expression will be up-regulated after activation of the cells. The expression of PD-L2 is relatively limited to antigen-presenting cells, such as activated macrophages and dendritic cells.

PD-L1 binds to PD-1 and B7-1 to inhibit the immune system, and many tumor cells and immune cells in tumor microenvironment express PD-L1. New studies have detected high expression of PD-L1 protein in human tumor tissues such as breast cancer, lung cancer, gastric cancer, intestinal cancer, renal cancer, melanoma, non-small cell lung cancer, colon cancer, bladder cancer, ovarian cancer, pancreatic cancer, liver cancer and others. Additionally, the expression level of PD-L1 is closely correlated with clinical condition and prognosis of patients.

As PD-L1 inhibits T cell proliferation through the second signaling pathway, blocking the binding of PD-L1 and PD-1 becomes a very promising target in the tumor immunotherapy field.

Currently there are several multinational pharmaceutical companies engaging in the study of monoclonal antibodies against PD-L1. These antibodies maximize the self-immune response of patients against tumors by blocking the binding of PD-1 and PD-L1 and sequentially kill tumor cells. Related patents are, for example, WO0139722, WO2013173223, WO2014195852, WO2013181634, WO2015048520, WO2015036511, US2014335093, WO2014100079, WO2014055897, U.S. Pat. No. 6,803,192B1, WO2014022758, U.S. Pat. No. 8,617,546B2 and WO2010089411A2.

The present invention provides a PD-L1 antibody with high affinity, high selectivity, and high biological activity.

SUMMARY OF THE INVENTION

The present invention provides a PD-L1 antibody or an antigen-binding fragment thereof, comprising any one of the CDR region sequences selected from the following or a mutant sequence thereof:

-   -   heavy chain variable region HCDR sequences shown in: SEQ ID NOs:         10-12 or SEQ ID NOs: 16-18; and light chain variable region LCDR         sequence shown in: SEQ ID NOs: 13-15 or SEQ ID NOs: 19-21;

Specifically, as follows:

-   -   HCDR1 selected from NDYWX₁ (SEQ ID NO: 10) or SYWMH (SEQ ID NO:         16);     -   HCDR2 selected from YISYTGSTYYNPSLKS (SEQ ID NO: 11) or RI         X₄PNSG X₅TSYNEKFKN (SEQ ID NO: 17):     -   HCDR3 selected from SGGWLAPFDY (SEQ ID NO: 12) or GGSSYDYFDY         (SEQ ID NO: 18);     -   LCDR1 selected from KSSQSLFYX₂SNQKX₃SLA (SEQ ID NO: 13) or         RASESVSIHGTHLMH (SEQ ID NO: 19);     -   LCDR2 selected from GASTRES (SEQ ID NO: 14) or AASNLES (SEQ ID         NO: 20);     -   LCDR3 selected from QQYYGYPYT (SEQ ID NO: 15) or QQSFEDPLT (SEQ         ID NO: 21);

Wherein X₁ is selected from N or T, X₂ is selected from R or H, X₃ is selected from N or H, X₄ is selected from H or G, and X₅ is selected from G or F.

In a preferred embodiment of the present invention, a PD-L1 antibody or antigen-binding fragment thereof, according to the present invention comprises a heavy chain variable region HCDR sequence selected from the group consisting of SEQ ID NO: 10, SEQ ID NO: 11, SEQ ID NO: 12, SEQ ID NO: 16, SEQ ID NO: 17 and SEQ ID NO: 18, or a mutant sequence thereof.

In another preferred embodiment of the present invention, a PD-L1 antibody or antigen-binding fragment thereof, according to the present invention comprises a light chain variable region LCDR sequence selected from the group consisting of SEQ ID NO: 13, SEQ ID NO: 14, SEQ ID NO: 15, SEQ ID NO: 19, SEQ ID NO: 20 and SEQ ID NO: 21, or a mutated sequence thereof.

In another preferred embodiment of the present invention, a PD-L1 antibody or antigen-binding fragment thereof according to the present invention, wherein the antibody light chain variable region further comprises a light chain FR region derived from murine κ chain, or a variant thereof, or a light chain FR region derived from murine λ-chain, or a variant thereof, wherein the antibody heavy chain variable region further comprises a heavy chain FR region derived from murine IgG1, or a variant thereof, or a heavy chain FR region derived from murine IgG2, or a variant thereof, or a heavy chain FR region derived from murine IgG3, or a variant thereof.

In another preferred embodiment of the present invention, a PD-L1 antibody or antigen-binding fragment thereof according to the present invention, wherein the antibody heavy chain variable region containing a murine-derived FR region is selected from the group consisting of SEQ ID NOs: 6 and 8, or a mutant sequence thereof, wherein the antibody light chain variable region containing a murine-derived FR region is selected from the group consisting of SEQ ID NOs: 7 and 9, or a mutant sequence thereof.

In another preferred embodiment of the present invention, a PD-L1 antibody or antigen-binding fragment thereof according to the present invention, wherein the antibody light chain further comprises a light chain constant region derived from murine κ chain, or a variant thereof, or a light chain constant region derived from murine λ chain, or a variant thereof, wherein the antibody heavy chain further comprises a heavy chain constant region derived from murine IgG1, or a variant thereof, or a heavy chain constant region derived from murine IgG2 or a variant thereof, or a heavy chain constant region derived from murine IgG3, or a variant thereof.

In another preferred embodiment of the present invention, a PD-L1 antibody or antigen-binding fragment thereof according to the present invention is a chimeric antibody. A PD-L1 chimeric antibody or the fragment thereof provided herein further comprises a heavy chain constant region derived from human IgG1, IgG2, IgG3, or IgG4, or a variant thereof, preferably comprises a heavy chain constant region derived from human IgG2, or IgG4, or IgG1 without ADCC (antibody-dependent cell-mediated cytotoxicity) via amino acid mutation.

In another preferred embodiment of the present invention, a PD-L1 antibody or antigen-binding fragment thereof according to the present invention is a humanized antibody or the fragment thereof. Preferably, the humanized antibody provided herein is the humanized antibody 9-2 or the humanized antibody 24D5, and the heavy chain FR sequence on the heavy chain variable region of the humanized antibody provided herein is derived from a human germline heavy chain, wherein: the heavy chain FR sequence on the heavy chain variable region of the humanized antibody 9-2 is derived from a combination sequence of a human germline heavy chain IGHV4-30-4*01 and hjh2, and comprises FR1, FR2, FR3 from human germline heavy chain IGHV4-30-4*01 and FR4 from hjh2; the heavy chain FR sequence on the heavy chain variable region of the humanized antibody 24D5 is derived from a combination sequence of a human germline heavy chain IGHV1-46*01 and hjh6.1, and comprises FR1, FR2, FR3 from human germline heavy chain IGHV1-46*01 and FR4 from hjh6.1. More preferably, the heavy chain FR sequence of the humanized antibody 9-2 provided herein has 0-10 amino acid back-mutations, preferably has one or more amino acid back-mutations selected from the group consisting of W47Y, V71R, G27Y, 148M, V67L, F78Y, S30T, and Q39K, more preferably has W47Y and V71R amino acid back-mutations; the heavy chain FR sequence of the humanized antibody 24D5 provided herein has 0-10 amino acid back-mutations, preferably has one or more amino acid back-mutations selected from the group consisting of T74K, R72V, M48I, M70L, R38Q, L83F, V68A, and V79A. Further, more preferably, the heavy chain variable region sequence of the humanized antibody is as follows: the heavy chain variable region sequence of the humanized antibody 9-2 is shown in SEQ ID NO: 22, or a variant thereof; or the heavy chain variable region sequence of the humanized antibody 24D5 is shown in SEQ ID NO: 24, or a variant thereof.

In another preferred embodiment of the present invention, a PD-L1 antibody or antigen-binding fragment thereof according to the present invention is a humanized antibody or the fragment thereof. Preferably, the humanized antibody provided herein is the humanized antibody 9-2 or the humanized antibody 24D5, the light chain FR sequence on the light chain variable region of the humanized antibody provided herein is derived from a human germline light chain, wherein: the light chain FR sequence on the light chain variable region of the humanized antibody 9-2 is derived from a combination sequence of a human germline light chain IGKV4-1*01 and hjk4.1, and comprises FR1, FR2 and FR3 from human germline light IGKV4-1*01 and FR4 from hjk4.1: the light chain FR sequence on the light chain variable region of the humanized antibody 24D5 is derived from a combination sequence of a human germline light chain IGKV7-3*01 and hjk2.1, and comprises FR1, FR2 and FR3 from human germline light IGKV7-3*01 and FR4 from hjk2.1. Preferably, the light chain FR sequence of the humanized antibody 9-2 provided herein has 0-10 amino acid back-mutations, more preferably has a P49S amino acid back-mutation. The light chain FR sequence of the humanized antibody 24D5 provided herein has 0-10 amino acid back-mutations, preferably has one or more amino acid back-mutations selected from the group consisting of Y91F, T22S and G72E, or introducing N85E deglycosylation mutation. Further, more preferably, the light chain variable region sequence of the humanized antibody provided herein is shown as follows: the light chain variable region sequence of the humanized antibody Ab-1 is shown in SEQ ID NO: 23, or a variant thereof; or the light chain variable region sequence of the humanized antibody Ab-2 is shown in SEQ ID NO: 25, or a variant thereof.

In another preferred embodiment of the present invention, provided is a PD-L1 antibody or antigen-binding fragment thereof, wherein the humanized antibody or antigen-binding fragment thereof is subjected to an affinity maturation design.

In another preferred embodiment of the present invention, provided is a PD-L1 antibody or antigen-binding fragment thereof, wherein X₁ is T, X₂ is H, X₃ is H, X₄ is G, X₅ is F.

In another preferred embodiment of the present invention, a PD-L1 antibody or antigen-binding fragment thereof comprises the humanized antibody variable region sequence as follows:

-   -   the heavy chain variable region sequence of the humanized         antibody 9-2 comprises SEQ ID NO: 26; and the light chain         variable region sequence of the humanized antibody 9-2 comprises         SEQ ID NO: 27;     -   the heavy chain variable region sequence of the humanized         antibody 24D5 comprises SEQ ID NO: 28; and the light chain         variable region sequence of the humanized antibody 24D5         comprises SEQ ID NO: 29.

In another preferred embodiment of the present invention, a PD-L1 antibody or antigen-binding fragment provided herein is humanized antibody or fragment thereof, wherein the heavy chain of humanized antibody further comprises a heavy chain constant region derived from human IgG1, IgG2, IgG3, or IgG4, or a variant thereof, preferably comprises a heavy chain constant region derived from human IgG2 or IgG4, more preferably comprises IgG4 heavy chain Fc region with F234A and L235A mutations; the humanized antibody further comprises a light chain constant region derived from human κ chain, human λ chain, or a variant thereof.

In another preferred embodiment of the present invention, a PD-L1 antibody or antigen-binding fragment thereof provided herein is the humanized antibody 9-2 or the humanized antibody 24D5, wherein the humanized antibody 9-2 comprises the heavy chain antibody sequence of SEQ ID NO: 30, and the light chain antibody sequence of SEQ ID NO: 32; wherein the humanized antibody 24D5 comprises the heavy chain antibody sequence of SEQ ID NO: 34, and the light chain antibody sequence of SEQ ID NO: 36.

The present invention further provides a pharmaceutical composition which comprises a therapeutically effective amount of the PD-L1 antibody or the antigen-binding fragment thereof described herein and one or more pharmaceutically acceptable carrier, diluent or excipient.

The present invention further provides a DNA molecule encoding the PD-L1 antibody or the antigen-binding fragment thereof described above.

The present invention further provides an expression vector comprising the DNA molecule encoding the PD-L1 antibody or the antigen-binding fragment thereof as described above.

The present invention further provides a host cell transformed with the expression vector as described above, wherein the host cell is selected from the group consisting of bacteria, yeast, and mammalian cells: preferably mammalian cells.

In another preferred embodiment of present invention, the host cell described herein is bacterium, preferably E. coli.

In another preferred embodiment of present invention, the host cell described herein is yeast, preferably Pichia pastoris.

In another preferred embodiment of present invention, a PD-L1 antibody or the antigen-binding fragment thereof is provided herein, wherein the antigen-binding fragment is Fab, Fv, scFv or F(ab′)2.

The present invention further provides use of the above PD-L1 antibody or the antigen-binding fragment thereof, or the pharmaceutical composition containing the same, in the preparation of a medicament for treatment of a PD-L1 mediated disease or disorder, wherein the disease is preferably a cancer, more preferably is a PD-L1-expressing cancer; and the cancer is preferably selected from the group consisting of breast cancer, lung cancer, stomach cancer, intestinal cancer, renal cancer, melanoma and bladder cancer; and most preferably is selected from the group consisting of non-small cell lung cancer, melanoma, bladder cancer and renal cancer.

The present invention further provides a method for treating or preventing a PD-1 mediated disease or disorder, comprising administering to a subject in need thereof a therapeutically effective amount of a PD-L1 antibody or the antigen-binding fragment thereof according to the invention, or the pharmaceutical composition comprising the same; wherein the disease is preferably a cancer, more preferably a PD-L1-expressing cancer: the cancer is preferably selected from the group consisting of breast cancer, lung cancer, stomach cancer, intestinal cancer, renal cancer, melanoma and bladder cancer; and most preferably is selected from the group consisting of non-small cell lung cancer, melanoma, bladder cancer and renal cancer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 : Schematic diagram of primers designed for constructing a humanized clone

FIG. 2 : Schematic diagram of vectors for constructing a humanized clone

FIG. 3 : Stimulation of PBMC proliferation by a humanized antibody

DETAILED DESCRIPTION OF THE INVENTION Terms

In order to make the invention more readily understood, certain technical and scientific terms are specifically defined below. Unless specifically defined elsewhere in this document, all other technical and scientific terms used herein have the meaning commonly understood by one of ordinary skill in the art to which this invention belongs.

As used herein, the single-letter code and the three-letter code for amino acids are as described in J. Biol. Chem, 243, (1%8) p3558.

As used herein, “Antibody” refers to immunoglobulin, a tetra-peptide chain structure connected together by disulfide bonds between two identical heavy chains and two identical light chains. Different immunoglobulin heavy chain constant regions exhibit different amino acid compositions and rank orders, hence present different kinds of antigenicity. Accordingly, immunoglobulins can be divided into five categories, or referred to as immunoglobulin isotypes, namely IgM, IgD, IgG, IgA and IgE, the corresponding heavy chains are μ chain, δ chain, γ chain, α chain and ε chain, respectively. According to its hinge region amino acid composition and the number and location of heavy chain disulfide bonds, the same isotype of Ig can be divided into different sub-categories; for example, IgG can be divided into IgG1, IgG2, IgG3, and IgG4. Light chain can be divided into κ or λ chain considering different constant regions. Each of the five Ig isotypes can have κ or λ chain.

In the present invention, the antibody light chain variable region mentioned herein further comprises a light chain constant region, which comprises a human- or murine-derived κ chain, λ chain, or a variant thereof.

In the present invention, the antibody heavy chain variable region mentioned herein further comprises a heavy chain constant region, which comprises a human- or murine-derived IgG1, IgG2, IgG3, IgG4, or a variant thereof.

About 110 amino acid sequences adjacent to the N-terminus of the antibody heavy and light chains are highly variable, known as the variable region (Fv region): the rest of the amino acid sequences near the C-terminus are relatively stable, known as the constant region. Variable region comprises three hypervariable regions (HVR) and four relatively conserved framework regions (FR). The three hypervariable regions determine the specificity of the antibody, also known as complementarity determining region (CDR). Each light chain variable region (LCVR) and each heavy chain variable region (HCVR) is composed of three CDR regions and four FR regions, with sequential order from the amino terminus to the carboxyl terminus being: FR1, CDR1, FR2, CDR2, FR3, CDR3, and FR4. The three light chain CDRs refer to LCDR1, LCDR2, and LCDR3; and the three heavy chain CDRs refer to HCDR1, HCDR2 and HCDR3. The number and location of CDR region amino acid residues in LCVR and HCVR regions of the antibody or antigen binding fragment herein comply with the known Kabat numbering criteria (LCDR1-3, HCDE2-3), or comply with Kabat and Chothia numbering criteria (HCDR1).

The antibody of the present invention comprises a murine-derived antibody, a chimeric antibody and a humanized antibody, preferably a humanized antibody.

The term “murine-derived antibody” in the present invention refers to a monoclonal antibody against human PD-L1 prepared according to the knowledge and skills in the field. During the preparation, a test subject was injected with PD-L1 antigen and then a hybridoma expressing the antibody with desired sequences or functional characteristics was isolated. In a preferred embodiment of the present invention, the murine-derived PD-L1 antibody or antigen binding fragment thereof further comprises a light chain constant region derived from murine κ chain, λ chain, or a variant thereof, or further comprises a heavy chain constant region derived from murine IgG1, IgG2, IgG3 or IgG4, or a variant thereof.

The term “chimeric antibody”, is an antibody formed by fusing the variable region of a murine-derived antibody with the constant region of a human antibody, wherein the chimeric antibody can alleviate the immune response induced by the murine-derived antibody. In order to establish a chimeric antibody, a hybridoma secreting a specific murine-derived monoclonal antibody is first established. A variable region gene is cloned from mouse hybridoma cells and then a constant region gene of a human antibody is cloned as desired. The mouse variable region gene is ligated with human constant region gene to form a chimeric gene, which will then be inserted into a human vector, and finally the chimeric antibody molecule is expressed in a eukaryotic or prokaryotic industrial system. In a preferred embodiment of the present invention, the light chain variable region of PD-L1 chimeric antibody further comprises a light chain Fc region derived from human κ chain, λ chain, or a variant thereof. The heavy chain variable region of the PD-L1 chimeric antibody further comprises a heavy chain constant region derived from human IgG1, IgG2, IgG3, IgG4, or a variant thereof. The constant region of a human antibody is selected from the heavy chain constant region derived from human IgG1, IgG2, IgG3 or IgG4, or a variant thereof, and preferably comprises a heavy chain constant region derived from human IgG2 or IgG4, or IgG4 without ADCC (antibody-dependent cell-mediated cytotoxicity) via amino acid mutation.

The term “humanized antibody”, also known as CDR-grafted antibody, refers to an antibody generated by grafting murine CDR sequences into a variable region framework of a human antibody, namely, the sequence of a human germline antibody framework of a different type. Humanized antibody overcomes the disadvantageously strong antibody response induced by the chimeric antibody that carries a large amount of murine protein components. Such framework sequences can be obtained from public DNA databases covering germline antibody gene sequences or published references. For example, germline DNA sequences of human heavy and light chain variable region genes can be found in “VBase” human germline sequence database (available on web www.mrccpe.com.ac.uk/vbase), as well as in Kabat, E A, et al, 1991 Sequences of Proteins of Immunological Interest, 5th Ed. To avoid the decrease in activity caused by reducing the immunogenicity, the variable region frame sequence of the human antibody is subjected to a minimum back-mutation or repeated mutation to maintain the activity. The humanized antibody of the present invention also comprises a humanized antibody wherein the CDR affinity is further matured via phage display.

As used herein, “antigen-binding fragment” refers to Fab fragment. Fab′ fragment, F(ab′)2 fragment with antigen-binding activity, as well as Fv fragment scFv fragment binding with human PD-L1; it comprises one or more CDR regions of antibodies described in the present invention, selected from the group consisting of SEQ ID NOs:10-21. Fv fragment is a minimum antibody fragment comprising a heavy chain variable region, a light chain variable region, and all antigen-binding sites without a constant region. Generally, Fv antibody further comprises a polypeptide linker between the VH and VL domains and is capable of forming a structure required for antigen binding. Also, different linkers can be used to connect the variable regions of two antibodies to form a polypeptide, named single chain antibody or single chain Fv (scFv). As used herein, the term “binding with PD-L1” means capable of interacting with human PD-L1. As used herein, the term “antigen-binding sites of the present invention” refers to discontinuous, three-dimensional sites on the antigen, recognized by the antibody or the antigen-binding fragment of the present invention.

As used herein, the term “ADCC”, namely antibody-dependent cell-mediated cytotoxicity, refers to the cells expressing Fc receptors that directly kill the target cells coated by an antibody by recognizing the Fc segment of the antibody. ADCC effector function of the antibody can be reduced or eliminated by modifying the Fc segment in IgG. The modification refers to mutations on the antibody heavy chain constant region, such as mutations selected from N297A, L234A, L235A in IgG1: IgG2/4 chimera; or L234A/E235A mutations in IgG4.

As used herein, a fusion protein described in the present invention is a protein product obtained by co-expressing two genes via recombinant DNA technology. Recombinant PD-L1 extracellular domain Fc fusion protein is obtained by co-expressing a PD-L1 extracellular domain and a human antibody Fc fragment via recombinant DNA technology. The PD-L1 extracellular domain refers to the moiety of the PD-L1 outside cytomembrane, the sequence of which is the underlined region of SEQ ID NO: 4 below.

Methods for producing and purifying antibodies and antigen-binding fragments are well known in the art and can be found, for example, in Antibody Experimental Technology Guide of Cold Spring Harbor, Chapters 5-8 and 15. For example, mice can be immunized with human PD-L1, or fragments thereof, and the resulting antibodies can then be renatured, purified and sequenced using conventional methods well known in the art. Antigen-binding fragments can also be prepared by conventional methods. The antibody or the antigen-binding fragment of the present invention is genetically engineered to introduce one or more human framework regions (FRs) to a non-human derived CDR Human FR germline sequences can be obtained by aligning human antibody variable region from gene database and MOE software, from ImMunoGeneTics (IMGT) via their website http://imgt.cines.fr, or from The Immunoglobulin FactsBook, 20011SBN012441351.

The engineered antibody or antigen-binding fragment of the present invention can be prepared and purified using conventional methods. For example, cDNA sequences encoding a heavy chain (SEQ ID NO: 30) and a light chain (SEQ ID NO: 32) can be cloned and recombined into a GS expression vector. The recombined immunoglobulin expression vector can then stably transfect CHO cells. As a more recommended method well known in the art, mammalian expression system will make antibodies glycosylated, typically at the highly conserved N-terminus in the Fc region. Stable clones can be obtained through expression of an antibody specifically binding to human PD-L1. Positive clones can be expanded in a serum-free culture medium for antibody production in bioreactors. Culture medium, into which an antibody has been secreted, can be purified by conventional techniques. For example, the medium can be conveniently applied to a Protein A or G Sepharose™ FF column that has been equilibrated with a compatible buffer. The column is washed to remove nonspecific binding components. The bound antibody is eluted by pH gradient and the antibody fragments are detected by SDS-PAGE, and then pooled. The antibody can be filtered and concentrated using common techniques. Soluble aggregate and multimers can be effectively removed by common techniques, including size exclusion or ion exchange. The obtained product can be immediately frozen, for example at −70° C., or can be lyophilized.

“Administration” and “treatment,” as they apply to an animal, human, experimental subject, cell, tissue, organ, or biological fluid, refer to contacting an exogenous pharmaceutical, therapeutic, diagnostic agent, or composition with the animal, human, subject, cell, tissue, organ, or biological fluid. “Administration” and “treatment” can refer, e.g., to therapeutic, pharmacokinetic, diagnostic, research, and experimental methods. Treatment of a cell encompasses contacting a reagent with the cell, as well as contacting a reagent with a fluid, where the fluid is in contact with the cell. “Administration” and “treatment” also mean in vitro and ex vivo treatments, e.g., of a cell, by a reagent, diagnostic, binding compound, or by another cell. “Treatment,” as it applies to a human, veterinary, or a research subject, refers to therapeutic treatment, prophylactic or preventative measures, to research and diagnostic applications.

“Treat” means to administer a therapeutic agent, such as a composition comprising any of the binding compounds of the present invention, internally or externally to a patient having one or more disease symptoms for which the agent has known therapeutic activity. Typically, the agent is administered in an amount effective to alleviate one or more disease symptoms in the treated patient or population, whether by inducing the regression of or inhibiting the progression of such symptom(s) to any clinically measurable degree. The amount of a therapeutic agent that is effective to alleviate any particular disease symptom (also referred to “therapeutically effective amount”) can vary according to factors such as the disease state, age, and weight of the patient, and the ability of the drug to elicit a desired response in the patient. Whether a disease symptom has been alleviated can be assessed by any clinical measurement typically used by physicians or other skilled healthcare providers to assess the severity or progression status of that symptom. While an embodiment of the present invention (e.g., a treatment method or article of manufacture) may not be effective in alleviating the disease symptom(s) of interest in every patient, it should alleviate the target disease symptom(s) of interest in a statistically significant number of patients as determined by any statistical test known in the art such as the Student's t-test, the chi-square test, the U-test according to Mann and Whitney, the Kruskal-Wallis test (H-test). Jonckheere-Terpstra-test and the Wilcoxon-test.

“Conservative modification” or “conservative replacement or substitution” refers to substitutions of amino acids in a protein with other amino acids having similar characteristics (e.g. charge, side-chain size, hydrophobicity/hydrophilicity, backbone conformation and rigidity, etc.), such that the changes can frequently be made without altering the biological activity of the protein. Those of skill in this art recognize that, in general, single amino acid substitution in non-essential regions of a polypeptide does not substantially alter biological activity (see, e.g., Watson et al. (1987) Molecular Biology of the Gene, The Benjamin/Cummings Pub Co., p. 224 (4.sup.th Ed.)). In addition, substitutions of structurally or functionally similar amino acids are less likely to disrupt biological activity.

“Effective amount” encompasses an amount sufficient to ameliorate or prevent a symptom or sign of a medical condition. Effective amount also means an amount sufficient to allow or facilitate diagnosis. An effective amount for a particular patient or veterinary subject can vary depending on factors such as the condition being treated, the general health of the patient, the route and dose of administration and the severity of side effects. An effective amount can be the maximal dose or dosing regimen that avoids significant side effects or toxic effects.

“Exogenous” refers to substances that are produced outside an organism, cell, or human body, depending on the context. “Endogenous” refers to substances that are produced within a cell, organism, or human body, depending on the context.

“Homology” refers to sequence similarity between two polynucleotide sequences or between two polypeptides. When a position in both of the two compared sequences is occupied by the same base or amino acid monomer subunit, e.g., if a position in each of two DNA molecules is occupied by adenine, then the molecules are homologous at that position. The percent of homology between two sequences is a function of the number of matching or homologous positions shared by the two sequences divided by the number of positions compared and then multiplied by 100. For example, if 6 of 10 positions in two sequences are matched or homologous when the sequences are optimally aligned, then the two sequences are 60% homologous. Generally, the comparison is made when two sequences are aligned to give maximum percent homology.

As used herein, the expressions “cell,” “cell line,” and “cell culture” are used interchangeably and all such designations include progeny. Thus, the words “transformants” and “transformed cells” include the primary subject cell and cultures derived therefrom without considering the number of passages. It is also understood that all progeny may not be precisely identical in DNA content, due to deliberate or inadvertent mutations. Mutated progeny that have the same function or biological activity as screened for in the originally transformed cell are included. Where distinct designations are intended, it will be clear from the context.

As used herein, “polymerase chain reaction” or “PCR” refers to a procedure or technique in which minute amounts of a specific moiety of nucleic acid, RNA and/or DNA, are amplified as described in, e.g., U.S. Pat. No. 4,683,195. Generally, sequence information from or beyond the ends of the region of interest needs to be available, such that oligonucleotide primers can be designed; these primers will be identical or similar in sequence to the corresponding strands of the template to be amplified. The 5′ terminal nucleotides of the two primers can be identical with the ends of the material to be amplified. PCR can be used to amplify specific RNA sequences, specific DNA sequences from total genomic DNA, and cDNA transcribed from total cellular RNA, bacteriophage, or plasmid sequences, etc. See generally Mullis et al. (1987) Cold Spring Harbor Symp. Ouant. Biol. 51:263; Erlich, ed., (1989) PCR TECHNOLOGY (Stockton Press, N.Y.). As used herein, PCR is considered as one, but not the only, example of a nucleic acid polymerase reaction method for amplifying a nucleic acid test sample, comprising the use of a known nucleic acid as a primer and a nucleic acid polymerase to amplify or generate a specific moiety of the nucleic acid.

“Optional” or “optionally” means that the event or situation that follows can but does not necessarily occur, and the description includes the instances in which the event or circumstance does or does not occur. For example, “optionally comprises 1-3 antibody heavy chain variable regions” means the antibody heavy chain variable region with specific sequence can be, but not necessarily be present.

“Pharmaceutical composition” refers to a mixture comprising one or more compounds according to the present invention or a physiologically/pharmaceutically acceptable salt or prodrug thereof with other chemical components, as well as additional components such as physiologically/pharmaceutically acceptable carriers and excipients. The pharmaceutical composition aims at promoting the administration to an organism, facilitating the absorption of the active ingredient and thereby exerting a biological effect.

EXAMPLES AND TESTS

Hereinafter, the present invention is further described with reference to the examples. However, the scope of the present invention is not limited thereto. In the examples of the present invention, where specific conditions are not described, the experiments are generally conducted under conventional conditions as described in Antibody Technology Laboratory Manual and Molecular Cloning Manual of Cold Spring Harbor, or under conditions proposed by the material or product manufacturers. Where the source of the reagents is not specifically given, the reagents are commercially available conventional reagents.

Example 1. Preparation of the PD-L1 Antigen and the Detection Protein Design and Expression of the Protein

The full-length human PD-L1 gene (UniProt Programmed Cell Death1 Ligand1 (PD-L1) isoform1 (SEQ ID NO: 1), from Sino Biological Inc., (HG10084-M)) was used as the template for PD-L1 of the present invention to obtain the gene sequences encoding antigens and the detection proteins of the present invention. Optionally, recombined with the antibody heavy chain Fc fragment (e.g., human IgG1), cloned into pTT5 vector (Biovector, Cat #: 102762) or pTargeT™ vector (promega, A1410) respectively, transiently expressed in 293F cells (Invitrogen, R79007) or stable expressed in CHO-S cells (Invitrogen, k9000-20), and purified to obtain the antigen and detection proteins of the present invention. Human PD-1 gene was purchased from ORIGENE, No. SC117011, NCBI Reference Sequence: NM_005018.1.

1. Human PD-L1 Full Length Amino Acid Sequence

SEQ ID NO: 1 MRIFAVFIFM TYWHLLNAFT VTVPKDLYVV EYGSNMTIEC  KFPVEKQLDL AALIVYWEME DKNIIQFVHG EEDLKVQHSS YRQRARLLKD QLSLGNAALQ ITDVKLQDAG VYRCMISYGG ADYKRITVKV NAPYNKINQR ILVVDPVTSE HELTCQAEGY PKAEVIWTSS DHQVLSGKTT TTNSKREEKL FNVTSTLRIN

KQSDTHLEET

Double underlined portion represents a signal peptide (Signal peptide: from 1 to 18).

Underlined portion represents extracellular domain of PD-L1 (Extracellular domain: from 19 to 238), wherein, from 19 to 127 represents Ig-like V-type Domain, and from 133 to 225 represents Ig-like C2-type Domain.

Dotted line portion represents transmembrane region (Transmembrane domain: from 239 to 259).

Italic portion represents cytoplasmic domain (Cytoplasmic domain: from 260 to 290).

2. Immunogen: PD-L1 with his, PADRE Tag: PD-L1 (Extra Cellular Domain, Short of ECD)-PADRE-His6

SEQ ID NO: 2 FT VTVPKDLYVV EYGSNMTIEC KFPVEKQLDL AALIVYWEME DKNIIQFVHG EEDLKVQHSS YRQRARLLKD QLSLGNAALQ  ITDVKLQDAG VYRCMISYGG ADYKRITVKV NAPYNKINQR     ILVVDPVTSE HELTCQAEGY PKAEVIWTSS DHQVLSGKTT    TTNSKREEKL FNVTSTLRIN TTTNEIFYCT FRRLDPEENH

Underlined portion represents extracellular domain of PD-L1; Dotted line portion represents PADRE tag: Italic portion represents His6-tag.

3. PD-L1 with FLAG and HIS Tag (PD-L1 (ECD)-Flag-His6) was Obtained and was Used for the Performance Test of the Antibodies of the Present Invention.

SEQ ID NO: 3 FT VTVPKDLYVV EYGSNMTIEC KFPVEKQLDL AALIVYWEME  DKNIIQFVHG EEDLKVQHSS YRQRARLLKD QLSLGNAALQ ITDVKLQDAG VYRCMISYGG ADYKRITVKV NAPYNKINQR ILVVDPVTSE HELTCQAEGY PKAEVIWTSS DHQVLSGKTT TTNSKREEKL FNVTSTLRIN TTTNEIFYCT FRRLDPEENH

Underlined portion presents extracellular domain of PD-L1: Dotted line portion represents Flag-Tag-, Italic portion represents His6-tag.

4. PD-L1 Fc Fusion Protein: PD-L1 (ECD)-Fc, is Used as an Immuno Antigen or a Detection Reagent of the Present Invention.

VKL-PD-L1(ECD)-Fc(human IgG1) SEQ ID NO: 4 FTVTVPKDLYVVEYGSNMTIECKFPVEKQLDLAALIVYWEMEDKNIIQFV HGEEDLKVQHSSYRQRARLLKDQLSLGNAALQITDVKLQDAGVYRCMISY GGADYKRITVKVNAPYNKINQRILVVDPVTSEHELTCQAEGYPKAEVIWT SSDHQVLSGKTTTTNSKREEKLFNVTSTLRINTTTNEIFYCTFRRLDPEE NHTAELVIPELPLAHPPNER DKTHTCPPCPAPELLGGPSVFLFPPKPKDT LMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTY RVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYT LPPSREEMTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDS DGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK

Underlined portion represents extracellular domain of PD-L1; Italic portion represents human IgG Fc.

5. PD-1 Fc Fusion Protein: PD-1(ECD)-Fc, is Used for the Performance Test of Antibodies of the Present Invention.

SEQ ID NO: 5 PGWFLDSPDRPWNPPTFSPALLVVTEGDNATFTCSFSNTSESFVLNWYRM SPSNQTDKLAAFPEDRSQPGQDCRFRVTQLPNGRDFHMSVVRARRNDSGT YLCGAISLAPKAQIKESLRAELRVTERRAEVETAHPSPSPRPAGQFQTLV EPKSSDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVD VSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLN GKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSL TCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKS RWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK

-   -   Underlined portion represents extracellular domain of PD-1;         Italic portion represents hFc (human IgG1).

Example 2. Purification of PD-L1, PD-1 Recombinant Protein, Hybridoma Antibody and Recombinant Antibody

1. Purification Steps of Recombinant Protein PD-L1 with His and PADRE Tag: PD-L1(ECD)-PADRE-His6 (SEQ ID NO: 2)

The supernatant sample, containing expressed cells, was centrifuged at high speed to remove impurities, the buffer was exchanged to PBS, and imidazole was added to a final concentration of 5 mM. A nickel column was equilibrated with PBS solution containing 5 mM imidazole and washed with 2-5 column volumes. After that, the supernatant sample was loaded onto the nickel column (GE, 17-5318-01). The column was washed with PBS solution containing 5 mM imidazole until the A280 reading returned to baseline. Then the column was washed with PBS plus 10 mM imidazole to remove nonspecific bound proteins and the effluent was collected. The target protein was eluted with PBS solution containing 300 mM imidazole and the elution peak was collected. The collected eluate was concentrated and further purified by chromatography gel Superdex200 (GE), the mobile phase was PBS. The mismatch peak was removed and the elution peak was collected. The obtained protein was identified by electrophoresis, peptide mapping (Agilent, 6530 Q-TOF), and LC-MS (Agilent 6530-TOF), and the correct sample was aliquoted for use. The PD-L1 protein with His and PADRE tag (PD-L1 (ECD)-PADRE-His6 E (SEQ ID NO: 2)) was obtained and used as an immunogen for the antibody of the present invention.

2. Purification Steps of Recombinant Protein PD-L1 with His and Flag Tag: PD-L1 (ECD)-Flag-His6 (SEQ ID NO: 3)

The sample was centrifuged at high speed to remove impurities and concentrated to an appropriate volume. The protein eluted from the IMAC column, as described above, was loaded onto a Flag affinity column (Sigma, A2220), which was equilibrated with 0.5×PBS and washed with 2-5 column volumes. The supernatant samples were loaded onto the column after removing impurities. The column was washed with 0.5×PBS until the A280 reading was reduced to baseline. Then, the column was washed with PBS containing 0.3 M NaCl, and the impurity protein was washed and collected. The target protein was eluted with 0.1 M acetic acid (pH 3.5-4.0) and collected, then the pH was adjusted to neutral. The collected eluate was concentrated and further purified by chromatography gel Superdex200 (GE), the mobile phase was PBS. The mismatch peak was removed and the elution peak was collected. The obtained protein was identified by electrophoresis, peptide mapping (Agilent, 6530 Q-TOF), and LC-MS (Agilent 6530-TOF), and the correct sample was aliquoted for use. The PD-L1 protein with His and Flag tag (PD-L1 (ECD)-Flag-His6 (SEQ ID NO: 3)) was obtained and used for performance testing of the antibodies in present invention.

3. Purification Steps of Fc Fusion Protein of PD-L1 and PD-1

The supernatant sample containing the expressed cells was centrifuged at high speed to remove impurities, concentrated to an appropriate volume, and then loaded onto a Protein A column (GE, 17-5438-01). The column was washed with 0.5×PBS until the A280 reading was reduced to baseline. The target protein was eluted with 100 mM sodium acetate (pH 3.0). 1M Tris™ HCl was used to neutralize the target protein. Then the neutralized protein was further purified by gel chromatography Superdex® 200 (GE), which was equilibrated with PBS. The mismatch peak was removed and the elution peak was collected, then the correct sample was aliquoted for use. This method was used to purify PD-L1 (ECD)-Fc (SEQ ID NO: 4) and PD-1 (ECD)-Fc (SEQ ID NO: 5). PD-1 (ECD)-Fc can be used as an antigen or detection reagent of the present invention and PD-1 (ECD)-Fc was used for performance testing of the antibody of the present invention.

Example 3. Preparation of Anti-humanPD-L1 Monoclonal Antibody

1. Immunization

The anti-human PD-L1 monoclonal antibody was produced by immunizing 6-week old female SJL white mice, (Beijing Vital River Laboratory Animal Technology Co., Ltd., animal production license number: SCXK (Beijing) 2012-0001).

Housing Environment: SPF level.

After the mice were purchased, the animals were kept in the laboratory for 1 week, 12/12 hours light/dark cycle, temperature 20-25° C., humidity 40-60%. After the mice had been acclimated to the environment, they were immunized according to two schemes (A and B), with 6-10 mice in each group. Immuno antigen was PD-L1 with His and PADRE tags ((PD-L1(ECD)-PADRE-His6 (SEQ ID NO: 2).

In Scheme A, Freund's adjuvant (sigma Lot Num: F5881/F5506) was for emulsification:

The first immunization was performed with Freund's complete adjuvant (CFA) and the other booster immunizations were performed with Freund's incomplete adjuvant (IFA). The ratio of antigen to adjuvant was 1:1, with dosing of 100 μg/mouse (first immunization) and 50 μg/mouse (booster immunization). On day 0, each mouse was intraperitoneal (IP) injected with 100 μg/mouse of the emulsified antigen, followed by immunization, once every two weeks for a total of 6-8 weeks.

In Scheme B, cross-immunization was performed alternatively with Titermax®: (sigma Lot Num: T2684) and Alum (Thremo Lot Num: 77161). The ratio of antigen to adjuvant (Titermax®) was 1:1 and the ratio of antigen to adjuvant (Alum) was 3:1, with dosing of 10-20 μg/mouse (first immunization) and 5 μg/mouse (booster immunization). On day 0, the mouse was intraperitoneal (IP) injected with 20 or 10 μg/mouse of the emulsified antigens, followed by immunization once a week. Titermax® and Alum were used alternately for a total 6-11 weeks. After four weeks of immunization, the antigen was administered via back or intraperitoneal injection, depending on the conditions of back lump and abdominal swelling.

2. Cell Fusion

Mice with higher serum antibody titers and the titers tending to plateau (See ELISA Test described in Test 1) were selected for splenocyte fusion. A shock immunization was performed by IP injection of 10 μg/mouse PD-L1-His 72 hours prior to splenocyte fusion. Hybridoma cells were obtained by fusing splenic lymphocytes with myeloma Sp2/0 cells (ATCC® CRL-8287™) using an optimized PEG-mediated fusion procedure. The hybridoma cells were resuspended in HAT complete medium (RPMI-1640 medium containing 20% FBS, 1×HAT and 1×OPI) and incubated in 96-well cell culture plates (1×10⁵/150 μl/well) at 37° C., 5% CO₂. On day 5 after fusion, HAT complete medium was added to cells, 50 μl/well, and then incubated at 5% CO₂ and 37° C. Seven to eight days after fusion, according to the density of the growing cells, the whole medium was changed to HT complete medium (RPMI-1640 medium containing 20% FBS, 1×HT and 1×OPI), 200 μl/well, and then incubated at 5% CO₂ and 37° C.

3. Screening for Hybridoma Cell

On day 10-11 after fusion, an ELISA assay was performed on PD-L1 binding according to the density of the growing cells (see Test 1). For the positive cells detected in the ELISA assay (Test 1), blockade in PD-L1/PD-1 binding was detected via ELISA analysis (see Test 2). Medium in the positive wells was changed and the positive cells were expanded to a 24-well plate depending on cell density. After re-testing, the cells transferred into the 24-well plate were used for breed conservation and first sub-cloning. The positive cells during the first sub-clone screening (see Test 1) were used for breed conservation and subjected to a second sub-cloning. The positive cells during the second sub-cloning were (see Test 1) used for breed conservation and protein expression. Hybridoma cells having blocking effect on PD-L1 and PD-1 binding (see Test 2) were obtained by multiple cell fusions.

Hybridoma clones 9-2 and 24D5 were obtained by a blocking experiment and a binding experiment, the antibody was further prepared by ascites method or serum-free cell culture method, and then purified by purification steps indicated in the examples for use in the test.

The murine antibody heavy chain variable region sequence of hybridoma clone 9-2 is indicated as follows

>9-2 mVH: murine antibody heavy chain variable region sequence of hybridoma clone 9-2 SEQ ID NO: 6 EVQLQESGPGLAKPSQTLSLTCSVAGYSIT NDYWN WIRKFPGNKLEYMG Y ISYTGSTYYNPSLKS RLSITRDTSKNQYYLQLNSVTAEDTAIYYCAR SGG WLAPFDY WGRGTTLTVSS >9-2 mVL: murine antibody light chain variable region sequence of hybridoma clone 9-2 SEQ ID NO: 7 DIVMSQSPSSLVVSVGEKVIMSC KSSQSLFYRSNQKNSLA WYQQKPGQSP KLLIY GASTRES GVPDRFTGSGSGTDFTVTISSVKAEDLAVYYCQQYYGY PYT FGGGTKLEIK

The order is FR1-CDR1-FR2-CDR2-FR3-CDR3-FR4, italic portion represents FR sequence, and underlined portion represents CDR sequence.

The murine antibody variable region sequence of hybridoma clone 24D5 is indicated as follows:

24D5-VH: murine antibody heavy chain variable region sequence of hybridoma clone 24D5 SEQ ID NO: 8 QVQLQQPGAELVKPGASVKLSCKASGYTFT SYWMH WVQQRPGQGLEWIG R IHPNSGGTSYNEKFKN RATLTVDKSSSTAYMQFSSLTSEDSAVYYSAR GG SSYDYFDY WGQGTTLTVSS 24D5-VL: murine antibody light chain variable region sequence of hybridoma clone 24D5 SEQ ID NO: 9 DIVLTQSPASLAVSLGQRATISC RASESVSIHGTHLMH WYQQKPGQPPKL LIY AASNLES GVPARFSGSGSETDFTLNIHPVEEEDATTYFC QQSFEDPL T FGAGTKLELK

The order is FR1-CDR1-FR2-CDR2-FR3-CDR3-FR4, italic portion represents FR sequence, and the underlined portion represents CDR sequence.

Heavy and light chain CDR sequences are as follows:

Heavy Chain Light Chain (9-2) HCDR1 NDYWN LCDR1 KSSQSLFYRSNQKNSLA SEQ ID NO: 38 SEQ ID NO: 40 HCDR2 YISYTGSTYYNPS LCDR2 GASTRES LKS SEQ ID NO: 14 SEQ ID NO: 11 HCDR3 SGGWLAPFDY LCDR3 QQYYGYPYT SEQ ID NO: 12 SEQ ID NO: 15 (24D5) HCDR1 SYWMH LCDR1 RASESVSIHGTHLM SEQ ID NO: 16 H SEQ ID NO: 19 HCDR2 RIHPNSGGTSYNE LCDR2 AASNLES KFKN SEQ ID NO: 20 SEQ ID NO: 39 HCDR3 GGSSYDYFDY LCDR3 QQSFEDPLT SEQ ID NO: 18 SEQ ID NO: 21

Wherein, when X₁ of SEQ ID NO: 10 is N, the sequence is SEQ ID NO: 38;

-   -   when X₄ of SEQ ID NO: 17 is H, X₅ of SEQ ID NO: 17 is G, the         sequence is SEQ ID NO: 39;     -   when X₂ of SEQ ID NO: 13 is R, X3 of SEQID NO: 13 is N, the         sequence is SEQ ID NO: 40.

Example 4. Humanization of Human Anti-PD-L1 Hybridoma Monoclonal Antibodies

1. Selection of Humanized Framework Sequences for Hybridoma Clone 9-2

After aligning with the IMGT human antibody heavy and light chain variable region gene database and MOE software, the heavy and light chain variable region genes with high homology to 9-2 and 24D5 were selected as templates, the CDRs of the two murine antibodies were grafted onto the corresponding human-derived template to form a variable region sequence in the order of FR1-CDR1-FR2-CDR2-FR3-CDR3-FR4. Wherein, amino acid residues were identified and annotated by the Kabat numbering system.

The humanized light chain template of the murine-derived antibody 9-2 is IGKV4-1*01 and hjk4.1, humanized heavy chain template is IGHV4-30-4*01 and hjh2, the sequence of humanized variable region is indicated as follows;

>9-2 hVH-CDR graft SEQ ID NO: 22 QVQLQESGPGLVKPSQTLSLTCTVSGGSIS NDYWN WIRQHPGKGLEWIG Y ISYTGSTYYNPSLKS RVTISVDTSKNQFSLKLSSVTAADTAVYYCAR SGG WLAPFDY WGRGTLVTVSS >9-2 hVL CDR graft SEQ ID NO: 23 DIVMTQSPDSLAVSLGERATINC KSSQSLFYRSNQKNSLA WYQQKPGQPP KLLIY GASTRES GVPDRFSGSGSGTDFTLTISSLQAEDVAVYYC QQYYGY PYT FGGGTKVEIK

The order is FR1-CDR1-FR2-CDR2-FR3-CDR3-FR4, italic portion represents FR sequence, and the underlined portion represents CDR sequence.

2. Selection of a Template and Back-Mutation Design for Hybridoma Clone 9-2. See Table 1 as Below:

TABLE 1 9_2_VL 9_2_VH h9_2_VL.1 Grafted h9_2_VH.1 Grafted h9_2_VL.1A P49S h9_2_VH.1A W47Y, V71R h9_2_VH.1B W47Y, V71R, G27Y, I48M, V67L h9_2_VH.1C W47Y, V71R, G27Y, I48M, V67L, F78Y, S30T h9_2_VH.1D W47Y, V71R, G27Y, I48M, V67L, F78Y, S30T, Q39K

For example, P49S indicates a back-mutation from P to S at position 49 according to Kabat numbering system.

Grafted indicates that the murine antibody CDR was implanted into human germline FR sequences.

TABLE 2 Humanized sequence combinations for murine antibody 9-2 h9_2_VH.1 h9_2_VH.1A h9_2_VH.1B h9_2_VH.1C h9_2_VH.1D h9_2_VL.1 9_2-1 9_2-2 9_2-3 9_2-4 9_2-5  h9_2_VL.1A 9_2-6 9_2-7 9_2-8 9_2-9 9_2-10

This table shows various sequence combinations of different mutations. For example, 9_2-2 indicates that two mutations (light chain h9_2_VL1 and heavy chain h9_2-VH.1A) are present on the humanized murine antibody 9-2, and so on.

3. Selection of Humanized Framework for the Hybridoma Clone 24D5

A serine is located on position 96 of PD-L1 hybridoma monoclonal antibody 24D5, while a conserved cysteine is located on FR3 of the germline gene, from which an intrachain disulfide bond is formed with a cysteine at position 22. We constructed a 24D5 chimeric antibody and another chimeric antibody of 24D5 with a back-mutation from serine to cysteine at position 96. The affinities of the two forms of chimeric antibodies are consistent with the affinity of the hybridoma antibody. Humanization of the antibody was performed by CDR graft strategy, and since the mutation on position 96 of 24D5 occurred on the skeleton, it did not affect the design scheme.

The humanized light chain template for the murine-derived antibody 24D5 is IGKV7-3*01 and hjk2.1, humanized heavy chain template is IGHV1-46*01 and hjh6.1, the sequence of humanized variable region is indicated as follows:

>24D5 Humanized heavy chain variable region VH.1 SEQ ID NO: 24 QVQLVQSGAEVKKPGASVKVSCKASGYTFT SYWMH WVRQAPGQGLEWMG R IGPNSGGTSYNEKFKN RVTMTRDTSTSTVYMELSSLRSEDTAVYYCAR GG SSYDYFDY WGQGTTVTVSS >24D5 Humanized light chain variable region VL.1 SEQ ID NO: 25 DIVLTQSPASLAVSPGQRATITC RASESVSIHGTHLMH WYQQKPGQPPKL LIY AASNLES GVPARFSGSGSGTDFTLTINPVEANDTANYYC QQSFEDPL TFGQGTKLEIK

The order is FR1-CDR1-FR2-CDR2-FR3-CDR3-FR4, italic portion represents FR sequence, and the underlined portion represents CDR sequence.

4. Selection of a Template and Back-Mutation Design for Hybridoma Clone 24D5. See Table 3 as Below:

TABLE 3 24D5_VL 24D5 _VH 24D5_VL.1 Grafted 24D5_VH.1 Grafted 24D5_VL.1A Y91F 24D5_VH.1A T74K 24D5_VL.1B Y91F, G72E 24D5_VH.1B T74K, R72V, M48I, M70L 24D5_VL.1C Y91F, G72E, 24D5_VH.1C T74K, R72V, M48I, M70L, T22S R38Q 24D5_VH.1D T74K, R72V, M48I, M70L, R38Q, L83F 24D5_VH.1E T74K, R72V, M48I, M70L, R38Q, L83F, V68A, V79A

For example, Y91F indicates a back-mutation from Y to F at position 91 according to Kabat numbering system.

Grafted indicates that the murine antibody CDR was implanted into human germline FR sequences.

TABLE 4 Humanized sequence combinations for murine antibody 24D5 h24D5_ h24D5_ h24D5_ h24D5_ VL.1 VL.1A VL.1B VL.1C h24D5_VH.1 1 2 3 4 h24D5_VH.1A 5 6 7 8 h24D5_VH.1B 9 10 11 12 h24D5_VH.1C 13 14 15 16 h24D5_VH.1D 17 18 19 20 h24D5_VH.1E 21 22 23 24

This table shows various sequence combinations of different mutations. For example, 5 indicates that two kinds of mutation (heavy chain h24D5_VH.1A and light chain h24D5_VL.1) are present on the humanized murine antibody 5, and so on.

Example 5. Construction of Humanized Clone

Primers were designed and VH/VK gene fragments of each humanized antibody were constructed by PCR and then inserted into the expression vector pHr (with signal peptide and constant region gene (CH1-FC/CL) fragment) via homologous recombination, to construct a full length of the antibody expression vector: VH-CH1-FC-pHr/VK-CL-pHr.

1. Primer Design:

The online software DNAWorks (v3.2.2) (http://helixweb.nih.gov/dnaworks/) was used to design multiple primers for synthesis of VH/VK gene fragments required for recombination: 5′-30 bp signal peptide+VH/VK+30 bp CH1/CL-3′. Rules for primer design: If there are two different amino acids between target gene 2 and the target gene 1, another primer comprising the mutation site was designed, as shown in FIG. 1 .

2. Fragment Splicing:

According to operating instructions for DNA polymerase from TaKaRa Company PrimeSTAR® GXL, using the primers designed above, VH/VK gene fragment containing the recombinant gene required was amplified by two-step PCR.

3. Construction of Expression Vector pHr (With Signal Peptide and Constant Region Gene (CH1-FC/L) Fragment) and Enzyme Digestion:

The expression vector pHr (with signal peptide and constant region gene (CH1-FC/CL) fragment) was designed and constructed by using some special restriction endonuclease, such as BsmBI, whose recognition sequence is different from the restriction site, as shown in FIG. 2 . BsmBI digested the vector, then digested fragments were gel extracted and stored for use.

4. Recombinant Construction of Expression Vector VH-CH1-FC-pHr/VK-CL-pHr

VH/VK containing gene fragments required for recombinant and expression vector pHr (with signal peptide and constant region gene (CH1-FC/CL) fragment) that had been digested with BsmBI were added into DH5H competent cells at a ratio of 3:1, incubated at 0° C. on ice for 30 min, heat-shocked at 42° C. for 90 s, combined with 5 volumes of LB medium, incubated at 37° C. for 45 min, coated on LB-Amp plate, and cultured at 37° C. overnight. A single clone was picked for sequencing and a clone of interest was obtained.

5. The plasmid was constructed according to the design of the present example, then the purified protein was expressed according to Example 2, and the affinity of the obtained protein was measured by the detection Example SPR.

6. Result:

The affinity of 9_2-2 was measured by BIACORE™ (Test 4), which was similar to the chimeric antibody, and only a slight increase in affinity was observed with more back-mutations. A good affinity was obtained by directly embedding the CDRs of antibody 24D5 into the humanized template, but the affinity of chimeric antibody itself was weaker than the hybridoma antibody. Introduction of N85E into the light chain for deglycosylation can improve homogeneity of the product and did not affect the affinity.

Finally, BIACORE™ was used to test the affinity of humanized variant having back-mutations to human PD-L1-his or hybridoma antibody, the humanized back-mutation sites and sequence combinations were selected as shown in Table 5:

TABLE 5 Humanized Kd Kd variants VH VL (Humanized) (Hybridoma) 9_2-2 VH.1 VL.1 5.68E−10 4.79E−10 W47Y/V71R 24D5-H CDR Graft VL.1 N85E 1.68E−10 6.68E−11

Example 6. Affinity Maturation of the Humanized Anti-PD-L1 Antibody

1. Construction of Humanized 9-2-2 and 24D5 Phagemid Vectors

The humanized 9-2-2 and 24D5 were constructed into the phagemid vector in scFv mode ((VH-3(GGGGS(SEQ ID NO: 41))-VL)) respectively, as a wild-type sequence (i.e., as an original or initial sequence relative to the mutant sequence obtained from the affinity maturation screening). Using overlap PCR, VH, 3 linkers (GGGGS(SEQ ID NO: 41), and VL were spliced and then ligated into the phagemid vector via NcoI and NotI cleavage sites.

2. Construction of Phage Display Library

The mutant library was constructed by using constructed wild-type scFv as template and codon-based primers. In the process of primer synthesis, each codon in the mutant region had 50% wild-type codons and a NNK of 50% (MNN for reverse primer), which was introduced into all CDR regions. The PCR fragment was digested with NcoI and NotI, ligated into the phagemid vector, and finally electrically transformed into E. coli TG1. Each codon-based primer was established as an independent library, in which 9-2-2 was divided into 7 libraries and 24D5 was divided into 8 libraries.

3. Library Panning

The biotinylated human PD-L1 (ECD) antigen and streptavidin magnetic beads were used for liquid-phase panning, and in each round of screening the antigen concentration was reduced relative to the previous round, after packaging phage particles used in the screening through the rescue of the library. After three rounds of panning, 250 clones of 9-2-2 and 24D5 antibodies were picked respectively, then subjected to phage ELISA to detect the binding activity, and the positive clones were sequenced.

4. Surface Plasmon Resonance (SPR) for Detection of Affinity

After the sequence analysis on the sequencing clones, the non-redundant sequences were transformed into full-length IG (γ1, κ) for mammalian cell expression after removal of the redundant sequence. The full length IG after affinity purification was determined by BIAcore™ X-100 instrument (GE Life Sciences) for affinity assay.

Confirmed the selected variable region sequence:

>9-2 hVH(T) SEQ ID NO: 26 QVQLQESGPGLVKPSQTLSLTCTVSGGSIS NDYW T WIRQHPGKGLEYIG Y ISYTGSTYYNPSLKS RVTISRDTSKNQFSLKLSSVTAADTAVYYCAR SGG WLAPFDY WGRGTLVTVSS

Wherein, CDR1 is SEQ ID NO: 10 when X₁ is T.

>9-2 hVL(H) SEQ ID NO: 27 DIVMTQSPDSLAVSLGERATINC KSSQSLFY H SNQK H SLA WYQQKPGQP PKLLIY GASTRES GVPDRFSGSGSGTDFTLTISSLQAEDVAVYYC QQYY GYPYT FGGGTKVEIK

Wherein, CDR1 is SEQ ID NO: 13 when X₂ is H and X₃ is H.

Affinity Maturation:

>24-D5 hVH(GF) SEQ ID NO: 28 QVQLVQSGAEVKKPGASVKVSCKASGYTFT SYWMH WVRQAPGQGLEWMG RI G PNSG F TSYNEKFKN RVTMTRDTSTSTVYMELSSLRSEDTAVYYCAR GGSSYDYFDY WGQGTTVTVSS

Wherein, CDR2 is SEQ ID NO: 17 when X₄ is G and X₅ is F.

>24-D5 hVL SEQ ID NO: 29 DIVLTQSPASLAVSPGQRATITC RASESVSIHGTHLMH WYQQKPGQPP KLLIY AASNLES GVPARFSGSGSGTDFTLTINPVEAEDTANYYC QQSF EDPLT FGQGTKLEIK

The order is FR1-CDR1-FR2-CDR2-FR3-CDR3-FR4, italic portion represents FR sequence, and the underlined portion represents CDR sequence, wherein the double underlined sites were obtained by affinity maturation after screening.

Example 7. Construction and Expression of Anti-PD-L1 Human IgG4 Type

Since PD-L1 is also expressed in activated T cells, the use of wild-type IgG1 constant regions will induce Fc-mediated effects, such as ADCC and CDC, leading to reduction in the activated T cells. Mutations in the IgG1 Fc such as D265A, N297A, L234A/L235A or L234F/L235A can reduce ADCC, and P331S or mutations near the position 331 can reduce CDC. Mutation of IgG2 and IgG2/4 Fc hybridization antibodies can also reduce ADCC and CDC effects. Mutant IgG4 was selected herein to obtain antibodies without ADCC and CDC. Thus, the clones obtained by affinity maturation were converted to IgG4 type, and the core hinge region of IgG4 contains the S228P mutation, which strengthens the linking of the disulfide bond in the core hinge region, thereby preventing the exchange of IgG4 Fab arms and greatly reducing the formation of hemi-molecule antibodies. F234A and L235A mutations (mAbs 4: 3, 310-318; May/June 2012) were further introduced. This form of IgG4 mutant antibody changes the CH2 domain and reduces the interaction with Fc receptors to achieve the effect of reducing ADCC activity. The purified 9-2 H2L10 antibody was expressed according to the present example and named HRP00049, and the expressed 24D5 29H1 GF was named HRP00052. These proteins will be further identified in the test case.

The affinity test for the IgG4 type mutant with the human PD-L1-his or rhesus monkey PD-L1-his is shown in Test 4, Table 6.

HRP00049: 9-2(H2/L10) IgG4 (AA)(S228P) Heavy chain: Heavy chain sequence of HRP00049 antibody SEQ ID NO: 30 QVQLQESGPGLVKPSQTLSLTCTVSGGSISNDYWTWIRQHPGKGLEYIG YISYTGSTYYNPSLKSRVTISRDTSKNQFSLKLSSVTAADTAVYYCARS GGWLAPFDYWGRGTLVTVSSASTKGPSVFPLAPCSRSTSESTAALGCLV KDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSSSLGT KTYTCNVDHKPSNTKVDKRVESKYGPPCPPCPAPEAAGGPSVFLFPPKP KDTLMISRTPEVTCVVVDVSQEDPEVQFNWYVDGVEVHNAKTKPREEQF NSTYRVVSVLTVLHQDWLNGKEYKCKVSNKGLPSSIEKTISKAKGQPRE PQVYTLPPSQEEMTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTT PPVLDSDGSFFLYSRLTVDKSRWQEGNVFSCSVMHEALHNHYTQKSLSL SLGK Gene sequence encoding HRP00049 antibody heavy chain: SEQ ID NO: 31 CAGGTGCAACTGCAGGAGAGCGGCCCCGGACTCGTGAAACCCTCCCAGA CCCTGAGCCTGACCTGTACCGTGAGCGGCGGCAGCATCAGCAACGACTA CTGGACTTGGATCAGGCAGCACCCCGGCAAAGGCCTGGAGTACATCGGC TACATCAGCTACACCGGCTCCACCTACTACAACCCCAGCCTGAAGTCCA GGGTGACCATCAGCCGGGACACCAGCAAGAACCAGTTCAGCCTGAAGCT GAGCAGCGTGACCGCTGCCGACACAGCCGTGTACTATTGTGCCAGAAGC GGCGGATGGCTGGCCCCTTTCGACTACTGGGGCAGAGGCACCCTGGTGA CCGTGAGCAGCGCTTCCACCAAGGGCCCATCGGTCTTCCCCCTGGCGCC CTGCTCCAGGAGCACCTCCGAGAGCACAGCCGCCCTGGGCTGCCTGGTC AAGGACTACTTCCCCGAACCGGTGACGGTGTCGTGGAACTCAGGCGCCC TGACCAGCGGCGTGCACACCTTCCCGGCTGTCCTACAGTCCTCAGGACT CTACTCCCTCAGCAGCGTGGTGACCGTGCCCTCCAGCAGCTTGGGCACG AAGACCTACACCTGCAACGTAGATCACAAGCCCAGCAACACCAAGGTGG ACAAGAGAGTTGAGTCCAAATATGGTCCCCCATGCCCACCATGCCCAGC ACCTGAGGCTGCTGGGGGACCATCAGTCTTCCTGTTCCCCCCAAAACCC AAGGACACTCTCATGATCTCCCGGACCCCTGAGGTCACGTGCGTGGTGG TGGACGTGAGCCAGGAAGACCCCGAGGTCCAGTTCAACTGGTACGTGGA TGGCGTGGAGGTGCATAATGCCAAGACAAAGCCGCGGGAGGAGCAGTTC AACAGCACGTACCGTGTGGTCAGCGTCCTCACCGTCCTGCACCAGGACT GGCTGAACGGCAAGGAGTACAAGTGCAAGGTCTCCAACAAAGGCCTCCC GTCCTCCATCGAGAAAACCATCTCCAAAGCCAAAGGGCAGCCCCGAGAG CCACAGGTGTACACCCTGCCCCCATCCCAGGAGGAGATGACCAAGAACC AGGTCAGCCTGACCTGCCTGGTCAAAGGCTTCTACCCCAGCGACATCGC CGTGGAGTGGGAGAGCAATGGGCAGCCGGAGAACAACTACAAGACCACG CCTCCCGTGCTGGACTCCGACGGCTCCTTCTTCCTCTACAGCAGGCTCA CCGTGGACAAGAGCAGGTGGCAGGAGGGGAATGTCTTCTCATGCTCCGT GATGCATGAGGCTCTGCACAACCACTACACACAGAAGAGCCTCTCCCTG TCTCTGGGTAAATGA Light chain: Light chain sequence of HRP00049 antibody SEQ ID NO: 32 DIVMTQSPDSLAVSLGERATINCKSSQSLFYHSNQKHSLAWYQQKPGQP PKLLIYGASTRESGVPDRFSGSGSGTDFTLTISSLQAEDVAVYYCQQYY GYPYTFGGGTKVEIKRTVAAPSVFIFPPSDEQLKSGTASVVCLLNNFYP REAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHK VYACEVTHQGLSSPVTKSFNRGEC Gene sequence encoding HRP00049 antibody light chain: SEQ ID NO: 33 GACATCGTGATGACCCAGAGCCCTGATAGCCTGGCTGTGAGCCTGGGC GAGAGAGCCACCATCAACTGCAAGAGCAGCCAGAGCCTGTTCTACCAT AGCAACCAGAAGCACAGCCTCGCCTGGTATCAGCAGAAGCCCGGCCAA CCCCCCAAGCTGCTGATCTACGGCGCCAGCACAAGAGAGAGCGGAGTG CCCGATAGGTTCAGCGGCAGCGGATCCGGCACCGATTTCACCCTGACC ATCAGCAGCCTGCAGGCCGAGGATGTGGCCGTGTACTACTGCCAGCAG TACTACGGCTACCCTTACACCTTCGGCGGCGGCACCAAGGTGGAGATC AAGCGTACGGTGGCTGCACCATCTGTCTTCATCTTCCCGCCATCTGAT GAGCAGTTGAAATCTGGAACTGCCTCTGTTGTGTGCCTGCTGAATAAC TTCTATCCCAGAGAGGCCAAAGTACAGTGGAAGGTGGATAACGCCCTC CAATCGGGTAACTCCCAGGAGAGTGTCACAGAGCAGGACAGCAAGGAC AGCACCTACAGCCTCAGCAGCACCCTGACGCTGAGCAAAGCAGACTAC GAGAAACACAAAGTCTACGCCTGCGAAGTCACCCATCAGGGCCTGAGC TCGCCCGTCACAAAGAGCTTCAACAGGGGAGAGTGTTGA HRP00052: 24D5(GF) IgG4 (AA) (S228P) Heavy chain: Heavy chain sequence of HRP00052 antibody SEQ ID NO: 34 QVQLVQSGAEVKKPGASVKVSCKASGYTFTSYWMHWVRQAPGQGLEWM GRIGPNSGFTSYNEKFKNRVTMTRDTSTSTVYMELSSLRSEDTAVYYC ARGGSSYDYFDYWGQGTTVTVSSASTKGPSVFPLAPCSRSTSESTAAL GCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPS SSLGTKTYTCNVDHKPSNTKVDKRVESKYGPPCPPCPAPEAAGGPSVF LFPPKPKDTLMISRTPEVTCVVVDVSQEDPEVQFNWYVDGVEVHNAKT KPREEQFNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKGLPSSIEKTIS KAKGQPREPQVYTLPPSQEEMTKNQVSLTCLVKGFYPSDIAVEWESNG QPENNYKTTPPVLDSDGSFFLYSRLTVDKSRWQEGNVFSCSVMHEALH NHYTQKSLSLSLGK Gene sequence encoding HRP00052 antibody heavy chain: SEQ ID NO: 35 CAGGTGCAACTGGTGCAGAGCGGTGCCGAGGTGAAGAAGCCTGGCGCA AGCGTGAAAGTGAGCTGCAAGGCCAGCGGCTACACCTTCACCAGCTAC TGGATGCACTGGGTGAGGCAGGCCCCTGGACAGGGCCTGGAGTGGATG GGCAGGATCGGGCCCAACAGTGGTTTCACTAGCTACAATGAAAAGTTC AAGAACAGGGTAACCATGACCAGGGACACCTCCACCAGCACAGTGTAT ATGGAGCTGAGCAGCCTGAGGAGCGAGGACACCGCCGTGTACTACTGT GCCAGAGGCGGCAGCAGCTACGACTACTTCGACTATTGGGGCCAGGGC ACCACCGTGACCGTGAGCAGTGCTTCCACCAAGGGCCCATCGGTCTTC CCCCTGGCGCCCTGCTCCAGGAGCACCTCCGAGAGCACAGCCGCCCTG GGCTGCCTGGTCAAGGACTACTTCCCCGAACCGGTGACGGTGTCGTGG AACTCAGGCGCCCTGACCAGCGGCGTGCACACCTTCCCGGCTGTCCTA CAGTCCTCAGGACTCTACTCCCTCAGCAGCGTGGTGACCGTGCCCTCC AGCAGCTTGGGCACGAAGACCTACACCTGCAACGTAGATCACAAGCCC AGCAACACCAAGGTGGACAAGAGAGTTGAGTCCAAATATGGTCCCCCA TGCCCACCATGCCCAGCACCTGAGGCTGCTGGGGGACCATCAGTCTTC CTGTTCCCCCCAAAACCCAAGGACACTCTCATGATCTCCCGGACCCCT GAGGTCACGTGCGTGGTGGTGGACGTGAGCCAGGAAGACCCCGAGGTC CAGTTCAACTGGTACGTGGATGGCGTGGAGGTGCATAATGCCAAGACA AAGCCGCGGGAGGAGCAGTTCAACAGCACGTACCGTGTGGTCAGCGTC CTCACCGTCCTGCACCAGGACTGGCTGAACGGCAAGGAGTACAAGTGC AAGGTCTCCAACAAAGGCCTCCCGTCCTCCATCGAGAAAACCATCTCC AAAGCCAAAGGGCAGCCCCGAGAGCCACAGGTGTACACCCTGCCCCCA TCCCAGGAGGAGATGACCAAGAACCAGGTCAGCCTGACCTGCCTGGTC AAAGGCTTCTACCCCAGCGACATCGCCGTGGAGTGGGAGAGCAATGGG CAGCCGGAGAACAACTACAAGACCACGCCTCCCGTGCTGGACTCCGAC GGCTCCTTCTTCCTCTACAGCAGGCTCACCGTGGACAAGAGCAGGTGG CAGGAGGGGAATGTCTTCTCATGCTCCGTGATGCATGAGGCTCTGCAC AACCACTACACACAGAAGAGCCTCTCCCTGTCTCTGGGTAAATGA Light chain: Light chain sequence of HRP00052 antibody SEQ ID NO: 36 DIVLTQSPASLAVSPGQRATITCRASESVSIHGTHLMHWYQQKPGQPP KLLIYAASNLESGVPARFSGSGSGTDFTLTINPVEAEDTANYYCQQSF EDPLTFGQGTKLEIKRTVAAPSVFIFPPSDEQLKSGTASVVCLLNNFY PREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEK HKVYACEVTHQGLSSPVTKSFNRGEC Gene sequence encoding HRP00052 antibody light chain: SEQ ID NO: 37 GACATCGTGCTGACCCAGAGTCCCGCCTCACTTGCCGTGAGCCCCGGT CAGAGGGCCACCATCACCTGTAGGGCCAGCGAGAGCGTGAGCATCCAC GGCACCCACCTGATGCACTGGTATCAACAGAAACCCGGCCAGCCCCCC AAACTGCTGATCTACGCCGCCAGCAACCTGGAGAGCGGCGTGCCCGCC AGGTTCAGCGGCTCCGGCAGCGGCACCGACTTCACCCTCACTATCAAC CCCGTGGAGGCCGAGGACACCGCCAACTACTACTGCCAGCAGAGCTTC GAGGACCCCCTGACCTTCGGCCAGGGCACCAAGCTGGAGATCAAGCGT ACGGTGGCTGCACCATCTGTCTTCATCTTCCCGCCATCTGATGAGCAG TTGAAATCTGGAACTGCCTCTGTTGTGTGCCTGCTGAATAACTTCTAT CCCAGAGAGGCCAAAGTACAGTGGAAGGTGGATAACGCCCTCCAATCG GGTAACTCCCAGGAGAGTGTCACAGAGCAGGACAGCAAGGACAGCACC TACAGCCTCAGCAGCACCCTGACGCTGAGCAAAGCAGACTACGAGAAA CACAAAGTCTACGCCTGCGAAGTCACCCATCAGGGCCTGAGCTCGCCC GTCACAAAGAGCTTCAACAGGGGAGAGTGTTGA

The underlined portion is a nucleotide sequence encoding a variable region sequence of the antibody heavy or light chain. The non-underlined portion is a nucleotide sequence encoding an antibody constant region sequence.

The performance and benefits of the present invention are verified by biochemical tests as indicated below.

Test 1. Binding ELISA for PD-L1

Microtitration plates were directly coated with 1 μg/ml (100 μg/well) of PD-L1(ECD)-Fc (SEQ ID NO: 4) and incubated at 4° C. overnight. Then the plates were blocked with 150 μl/well of PBS containing 5% Skim Milk (BD, 232100) and incubated at 4° C. overnight. The plates were then washed twice, 50 μl/well of cell supernatant was added to each well, and the plates were incubated at 37° C. for 2 h. The plates were washed three times, 50 μl/well of Peroxidase-AffiniPure Goat Anti-Human IgG (Jackson, 115-035-003) which was diluted with KPL Milk (KPL, 50-82-01) at a ratio of 1:5000 was added to each well, and the plates were incubated at 37° C. for 1 h. Next, the plates were washed four times, 50 μl/well of TMB was added to each well, and the plates were incubated at 37° C. for 10 min. The reaction was stopped by the addition of 50 μl/well of 1M H₂SO₄ to each well and the OD value was read on an ELISA microplate reader (BMG Labtech, NOVOStar) at a wavelength of 450 nm.

Test 2. Blocking ELISA Assay for the Binding Between PD-L1 and PD-1

The dilution of biotin (Dojindo Chemical, LK03: 3 samples) and avidin (Sigma. S2438-250UG) was 6% BSA (diluted with PBS containing 0.1% Tween®20), and PBS was used as coating solution. Microtitration plates were directly coated with 1 μg/ml (100 μg/well) of PD-L1(ECD)-Fc (SEQ ID NO: 4) and incubated at 4° C. overnight. The plate was washed three times and was blocked for 2 h at 37° C. with 3% BSA (diluted with PBS containing 0.1% Tween®20). The plate was washed three times and 50 μl/well of cell supernatant was added to each well. Then 50 μl/well of bio-PD-1-Fc (biotin-labeled PD-1-Fc, SEQ ID NO: 5, 2 μg/ml, PD-1-FC was labeled according to the method of Dojindo Chemical Kits Biotin Labeling Kit-NH2, LK03: 3 samples) was added to each well, well-mixed by vortex, and incubated at 37° C. for 1 h. The plates were washed 6 times, followed by addition of 50 μl/well Streptavidin-Peroxidase Polymer (S2438-250UG, Sigma, which was diluted at a ratio of 1:400), and incubated on shaker for 50 min at room temperature. The plate was washed 6 times, and then 100 μl/well of TMB was added, and incubated for 5-10 min at 37° C. Then the reaction was terminated with addition of 100 μl/well of 1M H₂SO₄. The absorbance value was read on microplate reader (BMG Labtech, NOVOStar) at 450 nm, and the IC₅₀ value for blocking the binding of PD-1 antibody to ligand PD-L1 was calculated. The blocking activity of the humanized antibody of the present invention in PD-L1/PD-1 binding is shown in Table 6 below.

A similar single point blocking assay was also used to screen hybridoma antibodies.

Test 3. Blockade in PD-L1 and B7.1 Binding by PD-L1 Antibody

This assay was similar to the blocking assay (Test 2) of PD-L1 antibody on the binding between PD-L1 and PD-1. Bio-human PD-1 (ECD) −FC in Test 2 was replaced with bio-human-B7.1 (human-B7.1, Sino Biological 10698-H03H-200), and the other steps were the same. In addition, we also detected the specific blockade of PD-L1 antibody in PD-L2-Fc (Q9BQ51, extracellular domain (aa20-aa220)) and PD-1 antibody binding similarly, and found that the antibody to be tested did not block the binding between PD-L2 and PD-1.

A similar single point blocking assay was used to screen hybridoma antibodies.

The blocking activity of humanized antibody of the present invention for PD-L1 and B7.1 binding and PD-L2 and PD-1 binding in are shown in Table 6 below.

TABLE 6 The blocking activity of the humanized antibody of the present invention huPD-L1-Fc/ huPD-LI-Fc/ huPD-L2-Fc/ Antibody to huPD-1 binding huB7.1-Fc binding huPD-1 binding be tested IC50 (ng/ml) IC50 (ng/ml) IC50 (ng/ml) HRP00052 114 69.6 NA HRP00049 174 113 NA MPDL3280A 126 92.9 NA NA indicates no blocking activity.

Test 4. Determination of the Affinity of PD-L1 Antibody HRP00049 and HRP00052 to PD-L1 Antigen by Biacore™ Assay

The anti-human capture antibody was covalently linked to the CM5 biochip (GE, BR-1000-12) according to the method described in the anti-human trapping kit (GE, BR-1008-39) instructions for affinity capturing the PD-L1 antibody of the present invention. Then, a series of concentrations of human PD-L1 antigen (Sino biological, 10084-H08H-200) were flowed through the surface of the biochip, and the reaction signal was detected in real time using a Biacore™ instrument (GE. Biacore™X100) to obtain the association and dissociation curves. Finally, the affinity values were obtained by fitting. After each cycle of dissociation was finished in the experiment, the biochip was washed and regenerated with regeneration solution in the anti-human capture kit (GE). The data obtained was analyzed by GE's BIA evaluation software using a 1:1 (Langmuir) binding model. Ka (kon), kd (koff) and KD values were determined by the assay. The affinity of hybridoma antibodies and humanized antibodies has been summarized in other examples. Table 7 below shows the affinities of the antibodies subjected to affinity maturation and the control antibody to human PD-L1 antigen (huPD-L1-his, Sino biological, 10084-H08H-200), cynomolgus PD-L1 antigen (Cyno PD-L1-his, Sino (90251-C08H-100) and murine PD-L1 antigen (Mouse PD-L1-his, Sino biological, 50010-M08H-100).

TABLE 7 Dissociation constants and species selectivity of HRP00049 and HRP00052 huPD-L1-his CynoPD-L1-his mousePD-L1 Antibody ka (1/Ms) kd (1/s) KD (M) ka (1/Ms) kd (1/s) KD (M) ka (1/Ms) kd (1/s) KD (M) HRP00052 1.77E+06 1.01E−04 5.70E−11 1.84E+06 1.06E−04 5.79E−11 NA NA NA HRP00049 9.52E+05 1.62E−04 1.70E−10 9.74E+05 1.67E−04 1.72E−10 NA NA NA MPDL3280A 1.15E+06 2.79E−04 2.43E−10 5.63E−09 3.48E+05 1.24E−03 3.56E−09

Test 5. In Vitro Cytology Test

Fresh human peripheral blood mononuclear cell (PBMC) proliferation assay affected by the antibody was performed to detect the cell activity with respect to the PD-L1 antibody.

Fresh human PBMCs (randomly collected from healthy persons) were adjusted to density of 2×10⁶/mL, inoculated in a 6-well plate at 2 ml/well, and incubated for 6 hours at 37° C., 5% CO₂. After the suspended cells were discarded, each well of adherent cells was mixed with 2 ml of RPMI1640 medium containing 100 ng/ml GM-CSF (granulocyte colony stimulating biological factor, Peprotech, AF-300-03) and 100 ng/ml IL-4 (Peprotech, AF-200-04). Two days after incubation, another 1 ml of RPMI1640 medium containing 100 ng/ml GM-CSF and 100 ng/ml IL-4 was added, then the cells were continually cultured for 2 days, followed by addition of 100 ng/ml TNF-α (tumor necrosis factor-α, Peprotech, AF-300-01 A) into each well, and cells were cultured for another 2 days to obtain mature dendritic cells. The dendritic cells and allogeneic T cells were centrifuged and resuspended at a concentration of 1×10⁶/ml and 1×10⁵/ml, respectively, and pipetted into a 96-well plate at 100 μl/well, followed by addition of 20 μl/well of antibody which was serially diluted into different concentrations with PBS, and then the cells were cultured in the incubator at 37° C., 5% CO₂ for 5 days. Thereafter, 100 μl was sampled for the detection of cell proliferation with CellTiter-Glo® Luminescent Cell Viability Assay kit. At the same time, the secretion of cytokine IFN-γ (interferon-γ) was determined.

Both HRP00052 and HRP00049 can effectively stimulate the secretion of cytokine IFN-γ. The same method was also used to detect the stimulation on PBMC proliferation (FIG. 3 ) and on the secretion of cytokine IFN-γ (Table 8) by humanized antibody. From FIG. 3 and Table 8, it was found that the humanized antibody of the present invention was more effective in stimulating the proliferation of PBMC and the secretion of cytokine IFN-γ than the positive control MPDL3280A (Atezolizumab, WHO Drug Information, Vol. 28, No. 4, 2014, P488).

TABLE 8 Both HRP00052 and HRP00049 stimulate PBMC to release cytokines IFN-γ antibody to be EC50 for cytokines IFN-γ tested release(ng/ml) MPDL3280A 72.1 HRP00052 18.7 HRP00049 34

Test 6. Activity of Antibody on Tuberculin-Stimulated PBMC Proliferation

The activity of the test antibody HRP00052, HRP00049 and reference antibody on tuberculin-stimulated PBMC proliferation in vitro was determined.

15 ml of fresh PBMCs, about 3×10⁷, were added into 20 μl tuberculin (Shanghai Biyou Biotechnology, cat #97-8800) and the mixture was incubated in the incubator for 5 days at the 37° C., 5% CO₂. On day 6, the cultured cells were centrifuged and resuspended into fresh medium with the density adjusted to 5×10⁵ cells/ml. 190 μl of resuspended cells were added into a 96-well plate, 10 μl/well of humanized antibody HRP00052 or HRP00049 was added into the corresponding well of the 96-well cell culture plate and 10 μl PBS was added in the control and blank group, respectively. Then, the cell culture plate was incubated in the incubator at the 37° C., 5% CO₂, and 72 hours later, PBMC proliferation (Promega, cat #G7571) and IFN-γ secretion (Neo Bioscience, cat #EHC102g) were determined. The results are shown in Table 9 below.

TABLE 9 Activity of the humanized antibody on tuberculin- stimulated PBMC proliferation Antibody to EC₅₀(ng/ml) for T cell EC₅₀(ng/ml) for be tested proliferation IFN-γ HRP00052 9.8 19.6 HRP00049 112 45.5 MPDL3280A 1464 353

Result: This experiment demonstrates that the humanized antibodies of the present invention have a stronger stimulating effect on PBMC proliferation which has previously been stimulated by exogenous antigen, and the characteristic has an unexpected effect when applied to the tumor treatment.

Test 7. Inhibitory Effect of PD-L1 Antibody HRP00052 on the Tumor Cell Growth in Mice Bearing U87MG Tumor

In this study, human glioblastoma U87MG cells were inoculated into the immunodeficient mice. After the tumor was formed, human PBMCs activated by anti-CD3 antibody were injected into tumor tissue to evaluate the effect of PD-L1 antibody in the treatment of mice subcutaneously injected with glioblastoma U87 MG tumor.

PBMCs were isolated from the blood provided by two volunteers, cultured and activated by anti-CD3 antibody (Miltenyi Biotec, 130-093-387). U87MG cells were inoculated subcutaneously in right ribs of SCID mice (Vital River 11400700081219), two weeks later, as the volume of tumor was ≥40 mm³, the mice with too large or too small body weight or tumor size were discarded. The remaining mice were randomly divided into groups according to the tumor volume. The two volunteer-derived PBMCs were stimulated with CD3 antibody, then were mixed at a ratio 1:1 and injected into the tumor tissue. Meanwhile, the subcutaneous injection of antibody or blank vector (5% glucose solution) was initiated. Administration was performed once on day 0, 7, 14 and 21, respectively, totally 4 times.

The result is shown in Table 10, indicating that the 3 mg/kg dose of PD-L1 antibody HRP00052 could significantly inhibit the growth of subcutaneous tumor of human malignant glioma U87MG.

TABLE 10 Effect of PD-L1 antibody on the treatment of mice subcutaneously grafted with glioma U87MG Day 0 Day 24 P Mean value ± Mean value ± (vs blank Group SEM(mm³) SEM(mm³) vector) % TGI Blank Vector 46.1 ± 7.6 875.3 ± 225.5 — — HRP00052 41.9 ± 4.7  355.3 ± 94.3 * 0.0460 62.21% (3 mg/kg) * P < 0.05, vs blank vector 

It is claimed:
 1. A method for treating a PD-L1 mediated cancer in a human subject in need thereof, the method comprising administering to the subject a therapeutically effective amount of an anti-PD-L1 antibody or antigen-binding fragment thereof, comprising a heavy chain variable region and a light chain variable region, wherein: (i) the heavy chain variable region comprises a heavy chain CDR1 (HCDR1) of NDYWX₁ (SEQ ID NO: 10), a heavy chain CDR2 (HCDR2) of YISYTGSTYYNPSLKS (SEQ ID NO: 11) and a heavy chain CDR3 (HCDR3) of SGGWLAPFDY (SEQ ID NO: 12); and the light chain variable region comprises a light chain CDR1 (LCDR1) of KSSQSLFYX₂SNQKX₃SLA (SEQ ID NO: 13), a light chain CDR2 (LCDR2) of GASTRES (SEQ ID NO: 14) and a light chain CDR3 (LCDR3) of QQYYGYPYT (SEQ ID NO: 15); wherein X₁ is N or T, X₂ is R or H, and X₃ is N or H; or (ii) the heavy chain variable region comprises a heavy chain CDR1 (HCDR1) of SYWMH (SEQ ID NO: 16), a heavy chain CDR2 (HCDR2) of RIX₄PNSG X₅TSYNEKFKN (SEQ ID NO: 17) and a heavy chain CDR3 (HCDR3) of GGSSYDYFDY (SEQ ID NO: 18); and the light chain variable region comprises a light chain CDR1 (LCDR1) of RASESVSIHGTHLMH (SEQ ID NO: 19), a light chain CDR2 (LCDR2) of AASNLES (SEQ ID NO: 20) and a light chain CDR3 (LCDR3) of QQSFEDPLT (SEQ ID NO: 21); wherein X₄ is H or G, and X₅ is G or F.
 2. The method according to claim 1, wherein the cancer is a PD-L1-expressing cancer selected from the group consisting of breast cancer, lung cancer, stomach cancer, intestinal cancer, renal cancer, melanoma, non-small cell lung cancer, glioblastoma and bladder cancer.
 3. The method according to claim 1, wherein the antibody light chain variable region further comprises a light chain framework (FR) region derived from murine κ chain, or murine λ-chain; and the antibody heavy chain variable region further comprises a heavy chain FR region derived from murine IgG1, murine IgG2 or murine IgG3.
 4. The method according to claim 3, wherein the antibody heavy chain variable region contains the heavy chain FR region derived from a murine heavy chain variable region having the amino acid sequence selected from the group consisting of SEQ ID NOs: 6 and 8, and the antibody light chain variable region contains a light chain FR region derived from a murine light chain variable region having the amino acid sequence selected from the group consisting of SEQ ID NOs: 7 and
 9. 5. The method according to claim 3, wherein the antibody light chain further comprises a light chain constant region derived from murine [k] kappa chain, or a light chain constant region derived from murine [Y] lambda chain; wherein the antibody heavy chain further comprises a heavy chain constant region derived from murine IgG1, or a heavy chain constant region derived from murine IgG2, or a heavy chain constant region derived from murine IgG3.
 6. The method according to claim 1, wherein the antibody or the antigen-binding fragment thereof is a chimeric antibody or a humanized antibody or a fragment thereof.
 7. The method according to claim 6, wherein the antibody is the humanized antibody 9-2 or the humanized antibody 24D5, wherein the heavy chain framework (FR) sequence on the heavy chain variable region of the humanized antibody 9-2 is derived from a combination sequence of a human germline heavy chain IGHV4-30-4*01 and human germline heavy chain hjh2, and comprises FR1, FR2, and FR3 from human germline heavy chain IGHV4-30-4*01 and FR4 from hjh2; or the heavy chain FR sequence on the heavy chain variable region of the humanized antibody 24D5 is derived from a combination sequence of human germline heavy chain IGHV1-46*01 and human germline heavy chain hjh6.1, and comprises FR1, FR2 and FR3 from human germline heavy chain IGHV1-46*01 and FR4 from hjh6.1.
 8. The method according to claim 7, wherein the heavy chain FR sequence of the humanized antibody 9-2 has 1-8 amino acid back-mutations selected from the group consisting of W47Y, V71R, G27Y, I48M, V67L, F78Y, S30T and Q39K; or wherein the heavy chain FR sequence of the humanized antibody 24D5 has 1-8 amino acid back-mutations selected from the group consisting of T74K, R72V, M48I, M70L, R38Q, L83F, V68A, and V79A.
 9. The method according to claim 7, wherein the heavy chain variable region sequence of the humanized antibody 9-2 comprises SEQ ID NO: 22 or a variant thereof, wherein the variant comprises 1-8 amino acid back-mutations selected from the group consisting of W47Y, V71R, G27Y, I48M, V67L, F78Y, S30T and Q39K; or the heavy chain variable region sequence of the humanized antibody 24D5 comprises SEQ ID NO: 24 or a variant thereof, wherein the variant comprises 1-8 amino acid back-mutations selected from the group consisting of T74K, R72V, M48I, M70L, R38Q, L83F, V68A, and V79A.
 10. The method according to claim 6, wherein the antibody is the humanized antibody 9-2 or the humanized antibody 24D5, wherein: the light chain framework (FR) sequence on the light chain variable region of the humanized antibody 9-2 is derived from a combination sequence of a human germline light chain IGKV4-1*01 and human germline light chain hjk4.1, and comprises FR1, FR2 and FR3 from human germline light chain IGKV4-1*01 and FR4 from hjk4.1, or the light chain FR sequence of the light chain variable region of the humanized antibody 24D5 is derived from a combination sequence of a human germline light chain IGKV7-3*01 and human germline light chain hjh2.1, and comprises FR1, FR2 and FR3 from IGKV7-3*01 and FR4 from hjk2.1.
 11. The method according to claim 10, wherein the light chain FR sequence of the humanized antibody 9-2 has a P49S amino acid back-mutation; or wherein the light chain FR sequence of the humanized antibody 24D5 has 1-3 amino acid back-mutations selected from the group consisting of Y91F, T22S and G72E, and optionally an N85E deglycosylation mutation.
 12. The method according to claim 10, wherein the light chain variable region sequence of the humanized antibody 9-2 comprises the amino acid sequence of SEQ ID NO: 23 or a variant thereof, wherein the variant comprises a P49S amino acid back-mutation; or the light chain variable region sequence of the humanized antibody 24D5 comprises the amino acid sequence of SEQ ID NO: 25 or a variant thereof, wherein the variant comprises 1-3 amino acid back-mutations selected from the group consisting of Y91F, T22S and G72E, and optionally an N85E deglycosylation mutation.
 13. The method according to claim 6, wherein X₁ is T, X₂ is H, X₃ is H, X₄ is G, and X₅ is F.
 14. The method according to claim 13, wherein the antibody is the humanized antibody 9-2 or the humanized antibody 24D5, and wherein the heavy chain variable region sequence of the humanized antibody 9-2 comprises SEQ ID NO: 26 and the light chain variable region sequence of the humanized antibody 9-2 comprises SEQ ID NO: 27; or the heavy chain variable region sequence of the humanized antibody 24D5 comprises SEQ ID NO: 28 and the light chain variable region sequence of the humanized antibody 24D5 comprises SEQ ID NO:
 29. 15. The method according to claim 14, wherein the heavy chain of the humanized antibody further comprises a heavy chain constant region derived from human IgG1, IgG2, IgG3, or IgG4; or wherein the light chain of the humanized antibody further comprises a constant region derived from human κ chain, or human λ chain.
 16. The method according to claim 15, wherein the heavy chain constant region comprises IgG4 heavy chain constant region with F234A and L235A mutations.
 17. The method according to claim 15, wherein the humanized antibody 9-2 comprises the heavy chain sequence of SEQ ID NO: 30 and the light chain sequence of SEQ ID NO: 32; or wherein the humanized antibody 24D5 comprises the heavy chain sequence of SEQ ID NO: 34 and the light chain sequence of SEQ ID NO:
 36. 18. A method for treating a PD-L1 mediated cancer in a human subject in need thereof, the method comprising administering to the subject a therapeutically effective amount of an anti-PD-L1 antibody or antigen-binding fragment thereof, comprising a heavy chain variable region and a light chain variable region, wherein: (i) the heavy chain variable region comprises a heavy chain CDR1 (HCDR1) of NDYWX₁ (SEQ ID NO: 10), a heavy chain CDR2 (HCDR2) of YISYTGSTYYNPSLKS (SEQ ID NO: 11) and a heavy chain CDR3 (HCDR3) of SGGWLAPFDY (SEQ ID NO: 12); and the light chain variable region comprises a light chain CDR1 (LCDR1) of KSSQSLFYX₂SNQKX₃SLA (SEQ ID NO: 13), a light chain CDR2 (LCDR2) of GASTRES (SEQ ID NO: 14) and a light chain CDR3 (LCDR3) of QQYYGYPYT (SEQ ID NO: 15); wherein X₁ is T, X₂ is H and X₃ is H; or (ii) the heavy chain variable region comprises a heavy chain CDR1 (HCDR1) of SYWMH (SEQ ID NO: 16), a heavy chain CDR2 (HCDR2) of RIX₄PNSG X₅TSYNEKFKN (SEQ ID NO: 17) and a heavy chain CDR3 (HCDR3) of GGSSYDYFDY (SEQ ID NO: 18); and the light chain variable region comprises a light chain CDR1 (LCDR1) of RASESVSIHGTHLMH (SEQ ID NO: 19), a light chain CDR2 (LCDR2) of AASNLES (SEQ ID NO: 20) and a light chain CDR3 (LCDR3) of QQSFEDPLT (SEQ ID NO: 21); wherein X₄ is G, and X₅ is F.
 19. The method according to claim 18, wherein the cancer is a PD-L1-expressing cancer selected from the group consisting of breast cancer, lung cancer, stomach cancer, intestinal cancer, renal cancer, melanoma, non-small cell lung cancer, glioblastoma and bladder cancer.
 20. A method for blocking the binding between PD-L1 and PD-1, the method comprising administering to a subject a therapeutically effective amount of an anti-PD-L1 antibody or antigen-binding fragment thereof, comprising a heavy chain variable region and a light chain variable region, wherein: (i) the heavy chain variable region comprises a heavy chain CDR1 (HCDR1) of NDYWX₁ (SEQ ID NO: 10), a heavy chain CDR2 (HCDR2) of YISYTGSTYYNPSLKS (SEQ ID NO: 11) and a heavy chain CDR3 (HCDR3) of SGGWLAPFDY (SEQ ID NO: 12); and the light chain variable region comprises a light chain CDR1 (LCDR1) of KSSQSLFYX₂SNQKX₃SLA (SEQ ID NO: 13), a light chain CDR2 (LCDR2) of GASTRES (SEQ ID NO: 14) and a light chain CDR3 (LCDR3) of QQYYGYPYT (SEQ ID NO: 15); wherein X₁ is N or T, X₂ is R or H, and X₃ is N or H; or (ii) the heavy chain variable region comprises a heavy chain CDR1 (HCDR1) of SYWMH (SEQ ID NO: 16), a heavy chain CDR2 (HCDR2) of RIX₄PNSG X₅TSYNEKFKN (SEQ ID NO: 17) and a heavy chain CDR3 (HCDR3) of GGSSYDYFDY (SEQ ID NO: 18); and the light chain variable region comprises a light chain CDR1 (LCDR1) of RASESVSIHGTHLMH (SEQ ID NO: 19), a light chain CDR2 (LCDR2) of AASNLES (SEQ ID NO: 20) and a light chain CDR3 (LCDR3) of QQSFEDPLT (SEQ ID NO: 21); wherein X₄ is H or G, and X₅ is G or F.
 21. The method of claim 20, wherein the subject is in need of a treatment of a PD-L1 mediated disease or disorder.
 22. The method of claim 21, wherein the subject is in need of a treatment of a cancer.
 23. The method of claim 22, wherein the cancer is a PD-L1-expressing cancer selected from the group consisting of breast cancer, lung cancer, stomach cancer, intestinal cancer, renal cancer, melanoma, non-small cell lung cancer, glioblastoma and bladder cancer. 